Quantum interference device, atomic oscillator, electronic device, and moving object

ABSTRACT

A quantum interference device includes: a gas cell in which metal atoms are sealed; a light emitting unit which emits light to the gas cell; a light receiving unit which receives the light penetrating the gas cell and outputs a light receiving signal; an input unit which inputs the light receiving signal; a light receiving circuit which processes the light receiving signal output from the input unit; a high frequency current generation unit which is arranged with the light emitting unit in a line, and generates high frequency current; and a first output unit which outputs the high frequency current output from the high frequency current generation unit to the light emitting unit, in which the gas cell is disposed between the input unit and the first output unit.

BACKGROUND

1. Technical Field

The present invention relates to a quantum interference device, anatomic oscillator, an electronic device, and a moving object.

2. Related Art

As an oscillator having oscillation characteristics with high accuracyin the long term, an atomic oscillator which oscillates based on atomicenergy transfer of an alkaline metal such as rubidium or cesium has beenknown (for example, see JP-A-2005-303641).

In general, the operating principle of the atomic oscillator is broadlydivided into a system using a double resonance phenomenon with light ormicrowaves, and a system using a quantum interference effect (coherentpopulation trapping: CPT) with two kinds of light beams having differentwavelengths, and recently, the atomic oscillator using the quantuminterference effect is expected to be mounted on various devices, sincethe oscillator can be miniaturized more than the oscillator using thedouble resonance phenomenon.

The atomic oscillator using the quantum interference effect, forexample, includes a gas cell in which gaseous metal atoms are sealed, asemiconductor laser which emits laser light having two kinds ofresonance light beams having different frequencies to metal atoms in thegas cell, and a photodetector which detects laser light penetrating thegas cell. In such an atomic oscillator, when a difference in thefrequencies of the two kinds of resonance light beams is a specificvalue, an electromagnetically induced transparency (EIT) phenomenon inwhich both of the two kinds of resonance light beams are not absorbedinto but penetrate the metal atoms in the gas cell occurs, but an EITsignal (atomic resonance signal) which is a sharp signal generated withthe EIT phenomenon is detected by the photodetector.

Herein, JP-A-2005-303641 discloses electrical connection of functionalblocks of the atomic oscillator.

However, since JP-A-2005-303641 does not disclose a positionrelationship between the gas cell and the functional blocks, an SN ratioof the EIT signal decreases depending on this position relationship, andan accuracy of an oscillation frequency of the atomic oscillatordecreases.

SUMMARY

An advantage of some aspects of the invention is to provide a quantuminterference device and an atomic oscillator which can improve an SNratio of an EIT signal, and to provide an electronic device and a movingobject including the quantum interference device with excellentreliability.

The invention can be implemented as the following forms or applicationexamples.

Application Example 1

This application example is directed to a quantum interference deviceincluding: a gas cell in which metal atoms are sealed; a light emittingunit which emits light to the gas cell; a light receiving unit whichreceives the light penetrating the gas cell and outputs a lightreceiving signal; an input unit which inputs the light receiving signal;a light receiving circuit which processes the light receiving signaloutput from the input unit; a high frequency current generation unitwhich is arranged with the light emitting unit in a line, and generateshigh frequency current; and a first output unit which outputs the highfrequency current output from the high frequency current generation unitto the light emitting unit, in which the gas cell is disposed betweenthe input unit and the first output unit.

With this configuration, it is possible to decrease a length of a wirebetween the input unit and the light receiving unit, to decrease anamount of noise mixed with the light receiving signal, to decrease alength of a wire between the first output unit and the light emittingunit, and to decrease an attenuation amount of the high frequencycurrent, and accordingly, it is possible to improve an SN ratio of anEIT signal, and to reliably detect the EIT signal. Therefore, it ispossible to provide a quantum interference device with high accuracy.

Application Example 2

In the quantum interference device according to the application example,it is preferable that the quantum interference device further includes:a bias current generation unit which is arranged with the light emittingunit in a line, and generates bias current to be supplied to the lightemitting unit; and a second output unit which outputs the bias currentoutput from the bias current generation unit to the light emitting unit,and the gas cell is disposed between the input unit and the secondoutput unit.

With this configuration, it is possible to decrease a length of a wirebetween the second output unit and the light emitting unit and todecrease an amount of noise mixed with the bias current, andaccordingly, it is possible to improve the SN ratio of the EIT signal.

Application Example 3

In the quantum interference device according to the application example,it is preferable that the high frequency current generation unit isdeviated from a linear line connecting the gas cell and the lightemitting unit.

With this configuration, it is possible to decrease a dimension of thedevice in a direction of the linear line and to realize miniaturization,compared to a case where the high frequency current generation unit isdisposed on the linear line.

Application Example 4

In the quantum interference device according to the application example,it is preferable that the high frequency current generation unit and thegas cell are arranged in a line.

With this configuration, it is possible to realize miniaturization.

Application Example 5

In the quantum interference device according to the application example,it is preferable that the first output unit is arranged in a directionin which the gas cell and the light emitting unit are arranged in aline, and disposed on the light emitting unit side with respect to thehigh frequency current generation unit.

With this configuration, it is possible to realize miniaturization.

Application Example 6

This application example is directed to an atomic oscillator includingthe quantum interference device according to the application example.

With this configuration, it is possible to decrease a length of a wirebetween the input unit and the light receiving unit, to decrease anamount of noise mixed with the light receiving signal, to decrease alength of a wire between the first output unit and the light emittingunit and to decrease an attenuation amount of the high frequencycurrent, and accordingly, it is possible to improve an SN ratio of anEIT signal, and to reliably detect the EIT signal. Therefore, it ispossible to provide a quantum interference device with high accuracy.

Application Example 7

This application example is directed to an electronic device includingthe quantum interference device according to the application example.

With this configuration, it is possible to provide an electronic devicehaving excellent reliability.

Application Example 8

This application example is directed to a moving object including thequantum interference device according to the application example.

With this configuration, it is possible to provide a moving objecthaving excellent reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a schematic view showing a schematic configuration of anatomic oscillator according to an embodiment of the invention.

FIG. 2 is a diagram illustrating an energy state of an alkaline metal.

FIG. 3 is a graph showing a relationship between a difference infrequencies of two light beams emitted from a light emitting unit andintensity of light detected by a light receiving unit and a lightreceiving circuit.

FIG. 4 is a cross-sectional view of the atomic oscillator shown in FIG.1.

FIG. 5 is a schematic view illustrating a light emitting unit and a gascell included in the atomic oscillator shown in FIG. 1.

FIG. 6 is a perspective view showing a first substrate, a secondsubstrate, and a third substrate included in the atomic oscillator shownin FIG. 1.

FIG. 7 is a plan view (including block diagram) showing a first unit, asecond unit, a first substrate, and units provided on the firstsubstrate, included in the atomic oscillator shown in FIG. 1.

FIG. 8 is a schematic view of a system configuration when an atomicoscillator according to the invention is used in a positioning systemusing a GPS satellite.

FIG. 9 is a diagram showing an example of a moving object according tothe invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, a quantum interference device, an atomic oscillator, anelectronic device, and a moving object according to the invention willbe described in detail with reference to embodiments shown in theaccompanying drawings.

1. Atomic Oscillator (Quantum Interference Device)

First, the atomic oscillator according to the invention (atomicoscillator including the quantum interference device according to theinvention) will be described. Hereinafter, an example in which thequantum interference device according to the invention is applied to theatomic oscillator will be described, but there is no limitation, and thequantum interference device according to the invention can also beapplied to, for example, a magnetic sensor, a quantum memory, or thelike, in addition to the atomic oscillator.

Embodiment

FIG. 1 is a schematic view showing a schematic configuration of anatomic oscillator according to a first embodiment of the invention. FIG.2 is a diagram illustrating an energy state of an alkaline metal, andFIG. 3 is a graph showing a relationship between a difference infrequencies of two light beams emitted from a light emitting unit andintensity of light detected by a light receiving unit and a lightreceiving circuit.

An atomic oscillator 1 shown in FIG. 1 is an atomic oscillator using aquantum interference effect.

As shown in FIG. 1 and FIG. 4, the atomic oscillator 1 includes a firstunit 2 which is a unit at a light emission side, a second unit 3 whichis a unit at a light detection side, optical components 41, 42, and 43provided between the units 2 and 3, a Peltier element 46, a temperaturesensor 47, a control unit 6 which controls the first unit 2, the secondunit 3, and the Peltier element 46, a first substrate 81, a secondsubstrate 82, a third substrate 83, a support plate (connection member)7, and an external package 5 containing these elements.

Herein, the first unit 2 includes a light emitting unit 21, a Peltierelement 24, a temperature sensor 25, and a first package 22 containingthese elements.

The second unit 3 includes a gas cell 31, a light receiving unit 38, aheater (heating unit) 33, a temperature sensor 34, a coil 35, and asecond package (housing) 36 containing these elements. The Peltierelement 46 and the temperature sensor 47 are provided in a predeterminedportion of the second package 36, for example.

First, the principle of the atomic oscillator 1 will be brieflydescribed.

As shown in FIG. 1, in the atomic oscillator 1, the light emitting unit21 emits an excitation light LL to the gas cell 31, and the excitationlight LL penetrating the gas cell 31 is detected by the light receivingunit 38 and a light receiving circuit 68.

A gaseous alkaline metal (metal atoms) is sealed in the gas cell 31. Asshown in FIG. 2, the alkaline metal has an energy level with athree-level system, and three states which are two ground states (groundstates 1 and 2) with different energy levels and an excitation state areintroduced. Herein, the ground state 1 is an energy state which is lowerthan the ground state 2.

The excitation light LL emitted from the light emitting unit 21 includestwo kinds of resonance light beams 1 and 2 having different frequencies.When the two kinds of resonance light beams 1 and 2 are emitted to thegaseous alkaline metal described above, light absorptance (lighttransmittance) of the resonance light beams 1 and 2 with respect to thealkaline metal changes, according to a difference between a frequency ω1of the resonance light 1 and a frequency ω2 of the resonance light 2ω1−ω2).

When the difference between the frequency ω1 of the resonance light 1and the frequency ω2 of the resonance light 2 ω1−ω2) coincides with afrequency equivalent to an energy difference between the ground state 1and the ground state 2, excitation from the respective ground states 1and 2 to the excitation state is stopped. At that time, both of theresonance light beams 1 and 2 are not absorbed into but penetrate thealkaline metal. Such a phenomenon is referred to as a CPT phenomenon oran electromagnetically induced transparency (EIT) phenomenon.

For example, when the light emitting unit 21 fixes the frequency ω1 ofthe resonance light 1 and changes the frequency ω2 of the resonancelight 2 and the difference between the frequency ω1 of the resonancelight 1 and the frequency ω2 of the resonance light 2 ω1−ω2) coincideswith a frequency ω0 equivalent to the energy difference between theground state 1 and the ground state 2, detection intensity of the lightreceiving unit 38 and the light receiving circuit 68 sharply increases,as shown in FIG. 3. Such a sharp signal is detected as an EIT signal(atomic resonance signal). The EIT signal has an eigenvalue determineddepending on the kinds of alkaline metal. Accordingly, the oscillatorcan be configured using the EIT signal.

Hereinafter, a specific configuration of the atomic oscillator 1according to the embodiment will be described.

FIG. 4 is a cross-sectional view of the atomic oscillator shown in FIG.1, FIG. 5 is a schematic view illustrating the light emitting unit andthe gas cell included in the atomic oscillator shown in FIG. 1, FIG. 6is a perspective view showing a first substrate, a second substrate, anda third substrate included in the atomic oscillator shown in FIG. 1, andFIG. 7 is a plan view (including block diagram) showing the first unit,the second unit, the first substrate, and units provided on the firstsubstrate, included in the atomic oscillator shown in FIG. 1. The crosssection of FIG. 4 is a cross section taken along line A-A of FIG. 6 andFIG. 7. Hereinafter, for the sake of convenience, the upper side inFIGS. 4 to 6 is referred to as an “upper portion” and the lower sidethereof is referred to as a “lower portion”. In FIG. 7, for the sake ofconvenience, an X axis and a Y axis are shown as two axes orthogonal toeach other, and a distal side of each arrow shown in the drawing is setas a “positive side” and a proximal side thereof is set as a “negativeside”. Hereinafter, for the sake of convenience, a direction parallel tothe X axis is referred to as an “X axis direction”, a direction parallelwith the Y axis is referred to as a “Y axis direction”, the positive Ydirection side (upper side in FIG. 7) is referred to as an “upperportion”, and the negative Y direction side (lower side in FIG. 7) isreferred to as an “lower portion”. The X axis direction is a directionparallel with an axis a of the excitation light LL, and the X axisdirection is a direction orthogonal to the axis a of the excitationlight LL or a direction parallel with the direction orthogonal to theaxis a of the excitation light LL. FIG. 7 shows only a part of wireswith an arrow.

As shown in FIG. 1 and FIG. 4, the atomic oscillator 1 includes thefirst substrate 81, the second substrate 82, and the third substrate 83on which the control unit 6 is separately mounted, and the support plate7 which supports the first unit 2 and the second unit 3 by the samesurface side.

The first unit 2, the second unit 3, the Peltier element 46, and thetemperature sensor 47 are electrically connected to the control unit 6through wires (not shown) of the first substrate 81, the secondsubstrate 82, and the third substrate 83, a flexible connector (notshown), and a connector (not shown) provided on the first substrate 81,the second substrate 82, and the third substrate 83. The first unit 2,the second unit 3, and the Peltier element 46 are driven and controlledby the control unit 6.

Hereinafter, each unit of the atomic oscillator 1 will be sequentiallydescribed in detail.

First Unit

As described above, the first unit 2 includes the light emitting unit21, the Peltier element 24, the temperature sensor 25, and the firstpackage 22 containing these elements.

Light Emitting Unit

The light emitting unit 21 has a function of emitting the excitationlight LL which excites the alkaline metal atoms in the gas cell 31.

More specifically, the light emitting unit 21 emits light including twokinds of light beams (resonance light 1 and resonance light 2) havingdifferent frequencies as described above, as the excitation light LL.

The frequency ω1 of the resonance light 1 allows the alkaline metal inthe gas cell 31 to excite (resonate) from the ground state 1 to theexcitation state described above.

The frequency ω2 of the resonance light 2 allows the alkaline metal inthe gas cell 31 to excite (resonate) from the ground state 2 to theexcitation state described above.

The light emitting unit 21 is not particularly limited as long as it canemit the excitation light LL described above, and a semiconductor lasersuch as a vertical cavity surface emitting laser (VCSEL) can be used,for example.

Peltier Element

The Peltier element (temperature adjusting element) 24 has a function ofheating and cooling the light emitting unit 21. Accordingly, thetemperature of the light emitting unit 21 is adjusted to a predeterminedtemperature. The temperature adjusting element for adjusting thetemperature of the light emitting unit 21 is not limited to the Peltierelement 24, and a heating resistor (heater) or the like is used, forexample.

The Peltier element 24 is electrically connected to a light emittingunit temperature control unit 64 of the control unit 6 which will bedescribed later, and is electrically controlled.

Temperature Sensor

The temperature sensor 25 detects the temperature of the light emittingunit 21. The driving of the Peltier element 24 described above iscontrolled based on the detected result of the temperature sensor 25.Accordingly, it is possible to maintain the temperature of the lightemitting unit 21 at a desirable temperature.

An installation position of the temperature sensor 25 is notparticularly limited, and an upper portion of an outer surface of thelight emitting unit 21 is used.

The temperature sensor 25 is not particularly limited, and variouswell-known temperature sensors such as a thermistor or a thermocouplecan be used.

The temperature sensor 25 is electrically connected to the lightemitting unit temperature control unit 64 of the control unit 6 whichwill be described later.

First Package

The first package 22 contains the light emitting unit 21, the Peltierelement 24, and the temperature sensor 25 described above.

The first package 22 includes a housing having a block-like externalshape and forms a box shape. The first package 22 is mounted on thesupport plate 7 which is fixed (connected) to a base plate 51 (see FIG.4) of the external package 5.

In addition, the first package 22 directly or indirectly supports thelight emitting unit 21, the Peltier element 24, and the temperaturesensor 25 from the inside thereof.

For example, a plurality of leads (not shown) are protruded from thefirst package 22, and these are electrically connected to the lightemitting unit 21, the Peltier element 24, and the temperature sensor 25through the wires. Each lead is electrically connected to apredetermined substrate of the first substrate 81, the second substrate82, and the third substrate 83 through a connector (not shown). As thisconnector, a flexible substrate or an element having a socket shape canbe used, for example.

A window portion 23 is provided on a wall of the first package 22 on thesecond unit 3 side. This window portion 23 is provided on an opticalaxis (axis a of excitation light LL) between the gas cell 31 and thelight emitting unit 21. The window portion 23 has permeability withrespect to the excitation light LL.

In the embodiment, the window portion 23 is a lens. Accordingly, theexcitation light LL can be emitted to the gas cell 31 without any waste.In addition, the window portion 23 has a function of setting theexcitation light LL as parallel light. That is, the window portion 23 isa collimating lens, and the excitation light LL in an internal space Sis parallel light. Accordingly, among the alkaline metal atoms existingin the internal space S, it is possible to increase the number ofalkaline metal atoms resonating by the excitation light LL emitted fromthe light emitting unit 21. As a result, it is possible to increase theintensity of the EIT signal.

The window portion 23 is not limited to a lens, as long as it haspermeability with respect to the excitation light LL, and an opticalcomponent other than a lens may be used, or a simple plate-shaped memberhaving optical transparency may be used, for example. In this case, thelens having such a function may be, for example, provided between thefirst package 22 and the second package 36, in the same manner as thatof the optical components 41, 42, and 43 which will be described later.

The configuration material in a portion of the first package 22 otherthan the window portion 23 is not particularly limited, and ceramics,metals, or resins can be used, for example.

Herein, in a case where the portion of the first package 22 other thanthe window portion 23 is configured with a material having permeabilitywith respect to the excitation light, the portion of the first package22 other than the window portion 23 and the window portion 23 can beintegrally formed. In a case where the portion of the first package 22other than the window portion 23 is configured with a material nothaving permeability with respect to the excitation light, the portion ofthe first package 22 other than the window portion 23 and the windowportion 23 are separately formed, and may be bonded to each other by awell-known bonding method.

The inside of the first package 22 is preferably an airtight space.Accordingly, the inside of the first package 22 can be areduced-pressure state or an inert gas sealed state, and as a result, itis possible to improve properties of the atomic oscillator 1.

According to the first package 22, it is possible to allow the emissionof the excitation light from the light emitting unit 21 to the outsideof the first package 22, and to contain the light emitting unit 21, thePeltier element 24, and the temperature sensor 25 in the first package22.

Second Unit

As described above, the second unit 3 includes the gas cell 31, thelight receiving unit 38, the heater 33, the temperature sensor 34, thecoil 35, and the second package 36 containing these elements.

Gas Cell

The alkaline metal such as gaseous rubidium, cesium, or sodium is sealedin the gas cell 31. In addition, noble gas such as argon or neon, orinert gas such as nitrogen may be sealed in the gas cell 31 as buffergas, if necessary, with the alkaline metal gas.

For example, as shown in FIG. 5, the gas cell 31 includes a main bodyportion 311 including a columnar penetration hole 311 a, and a pair ofwindow portions 312 and 313 which blocks both openings of thepenetration hole 311 a. Accordingly, the internal space S describedabove with the alkaline metal sealed therein is formed.

The material configuring the main body portion 311 is not particularlylimited, and a metal material, a resin material, a glass material, asilicon material, or a quartz crystal is used, but the glass materialand the silicon material are preferably used, from a viewpoint ofworkability or bonding of the window portions 312 and 313.

The window portions 312 and 313 are airtightly bonded to the main bodyportion 311. Accordingly, the internal space S of the gas cell 31 can beset as an airtight space.

The bonding method of the main body portion 311 and the window portions312 and 313 is determined depending on the kinds of the configurationmaterials and is not particularly limited, but a bonding method using anadhesive, a direct bonding method, or an anodic bonding method can beused, for example.

The material configuring the window portions 312 and 313 is notparticularly limited, as long as it has permeability with respect to theexcitation light LL described above, and a silicon material, a glassmaterial, or a quartz crystal is used, for example.

Each of the window portions 312 and 313 has permeability with respect tothe excitation light LL from the light emitting unit 21 described above.The excitation light LL incident on the inside of the gas cell 31penetrates one window portion 312, and the excitation light LL emittedfrom the inside of the gas cell 31 penetrates the other window portion313.

The gas cell 31 is heated by the heater 33, and the temperature thereofis adjusted to a predetermined temperature.

Light Receiving Unit and Light Receiving Circuit

The light receiving unit 38 and the light receiving circuit 68 have afunction of detecting the intensity of the excitation light LL(resonance light beams 1 and 2) penetrating the inside of the gas cell31. In this case, the light receiving unit 38 has a function ofreceiving the excitation light LL penetrating the inside of the gas cell31, that is, a function of photoelectric conversion. The light receivingcircuit 68 has a function of converting a light receiving signal of thelight receiving unit 38, that is, current output from the lightreceiving unit 38 into a voltage and amplifying the voltage. That is,the light receiving circuit 68 includes a current-voltage conversioncircuit (IV conversion circuit) which converts the current into thevoltage.

The light receiving unit 38 is not particularly limited, as long as itcan receive the excitation light LL described above, and a photodetector(light receiving element) such as a solar cell or a photodiode can beused, for example.

Herein, as shown in FIG. 7, a connector 195 is installed on the firstsubstrate 81, and the connector 195 and the light receiving unit 38 areelectrically connected to each other by a flexible connector (notshown). The connector 195 and the light receiving circuit 68 areelectrically connected to each other by a wire 93 of the first substrate81. The connector 195 is an input unit to which the light receivingsignal of the light receiving unit 38 is input, and the light receivingsignal input from the connector 195 is subjected to a process in thelight receiving circuit 68 as will be described later.

Heater

The heater 33 has a function of heating the gas cell 31 described above(more specifically, alkaline metal in the gas cell 31). Accordingly, itis possible to maintain the alkaline metal in the gas cell 31 in agaseous state with a desirable concentration.

The heater 33 is driven by the supply of the power, that is, performsheating by electrical connection, and is configured with a heatingresistor provided on an outer surface of the gas cell 31, for example.The heating resistor is formed using a chemical vapor deposition method(CVD) such as plasma CVD or thermal CVD, a dry plating method such asvacuum vapor deposition, or a sol-gel method.

Herein, when the heating resistor is provided on an incident portion oran emitting portion of the excitation light LL on the gas cell 31, theheating resistor is configured with a material having permeability withrespect to the excitation light, specifically, a transparent electrodematerial such as oxides such as indium tin oxide (ITO), indium zincoxide (IZO), In₃O₃, SnO₂, Sb-containing SnO₂, or Al-containing ZnO, forexample.

The heater 33 is not particularly limited, as long as it can heat thegas cell 31, and may not come in contact with the gas cell 31. The gascell 31 may be heated using the Peltier element, instead of the heater33, or in combination use with the heater 33.

The heater 33 is electrically connected to a cell temperature controlunit 62 of the control unit 6 which will be described later, and iselectrically controlled.

Temperature Sensor

The temperature sensor 34 detects the temperature of the heater 33 orthe gas cell 31. The amount of heat generation of the heater 33described above is controlled, based on the detected result of thetemperature sensor 34. Accordingly, it is possible to maintain thetemperature of the alkaline metal atoms in the gas cell 31 at adesirable temperature.

An installation position of the temperature sensor 34 is notparticularly limited, and an upper portion of the heater 33, or an upperportion of the outer surface of the gas cell 31 may be used.

The temperature sensor 34 is not particularly limited, and variouswell-known temperature sensors such as a thermistor or a thermocouplecan be used.

The temperature sensor 34 is electrically connected to the celltemperature control unit 62 of the control unit 6 which will bedescribed later.

Coil

The coil 35 has a function of generating a magnetic field in a direction(parallel direction) along the axis a of the excitation light LL in theinternal space S, by electrical connection. Accordingly, it is possibleto improve resolution by widening a gap between different degeneratedenergy levels of the alkaline metal atoms existing in the internal spaceS due to Zeeman splitting, and to decrease a line width of the EITsignal. As a result, it is possible to increase an accuracy of anoscillation frequency of the atomic oscillator 1.

The magnetic field generated by the coil 35 may be any magnetic fieldsuch as a DC magnetic field or an AC magnetic field, or may be amagnetic field where a DC magnetic field and an AC magnetic field aresuperimposed onto each other.

An installation position of the coil 35 is not particularly limited andis not shown. The coil may be provided to be wound along an outerperiphery of the gas cell 31 so as to have a solenoid typeconfiguration, or the pair of coils may face each other with the gascell 31 interposed therebetween so as to have a Helmholtz typeconfiguration.

The coil 35 is electrically connected to a magnetic field control unit63 of the control unit 6 which will be described later, through a wire(not shown). Accordingly, it is possible to perform the electricalconnection with respect to the coil 35.

Second Package

The second package 36 contains the gas cell 31, the light receiving unit38, the heater 33, the temperature sensor 34, and the coil 35 describedabove.

The second package 36 includes a housing having a block-like externalshape and forms a box shape. The second package 36 is mounted on thesupport plate 7 which is fixed (connected) to the base plate 51 (seeFIG. 4) of the external package 5.

In addition, the second package 36 directly or indirectly supports thegas cell 31, the light receiving unit 38, the heater 33, the temperaturesensor 34, and the coil 35 from the inside thereof.

For example, a plurality of leads (not shown) are protruded from thesecond package 36, and these are electrically connected to the gas cell31, the light receiving unit 38, the heater 33, the temperature sensor34, and the coil 35 through the wires. Each lead is electricallyconnected to a predetermined substrate of the first substrate 81, thesecond substrate 82, and the third substrate 83 through a connector (notshown). As this connector, a flexible substrate or an element having asocket shape can be used, for example.

A window portion 37 is provided on a wall of the second package 36 onthe first unit 2 side. This window portion 37 is provided on an opticalaxis (axis a) between the gas cell 31 and the light emitting unit 21.The window portion 37 has permeability with respect to the excitationlight LL.

The window portion 37 is not limited to have optical transparency, aslong as it has permeability with respect to the excitation light, andfor example, may be an optical component such as a lens, a polarizingplate, or a λ/4 wavelength plate.

The configuration material in a portion of the second package 36 otherthan the window portion 37 is not particularly limited, and ceramics,metals, or resins can be used, for example.

Peltier Element and Temperature Sensor

Peltier Element

The Peltier element (temperature adjusting element) 46 has a function ofheating and cooling the second package 36. Accordingly, the temperatureof the second package 36 is adjusted to a predetermined temperature. Thetemperature adjusting element for adjusting the temperature of thesecond package 36 is not limited to the Peltier element 46, and aheating resistor (heater) or the like is used, for example.

The Peltier element 46 is electrically connected to a packagetemperature control unit 65 of the control unit 6 which will bedescribed later, and is electrically controlled.

Temperature Sensor

The temperature sensor 47 detects the inside temperature of the secondpackage 36. The driving of the Peltier element 46 described above iscontrolled based on the detected result of the temperature sensor 47.Accordingly, it is possible to maintain the temperature of the secondpackage 36 at a desirable temperature.

An installation position of the temperature sensor 47 is notparticularly limited, and an upper portion of an outer surface of thesecond package 36 is used, for example.

The temperature sensor 47 is not particularly limited, and variouswell-known temperature sensors such as a thermistor or a thermocouplecan be used.

The temperature sensor 47 is electrically connected to the packagetemperature control unit 65 of the control unit 6 which will bedescribed later.

Optical Component

The plurality of optical components 41, 42, and 43 are disposed betweenthe first package 22 and the second package 36. The plurality of opticalcomponents 41, 42, and 43 are provided on the optical axis (axis a)between the light emitting unit 21 in the first package 22 describedabove and the gas cell 31 in the second package 36 described above.

In the embodiment, the optical components 41, 42, and 43 are disposed inthis order, from the first package 22 side to the second package 36side. The optical components 41, 42, and 43 are installed on the baseplate 51 (see FIG. 4) of the external package 5. As a method of holdingthe optical components 41, 42, and 43, a method of providing threerecesses on the base plate 51 and inserting the optical components 41,42, and 43 into respective recesses is used, for example.

The optical component 41 is a λ/4 wavelength plate. Accordingly, whenthe excitation light from the light emitting unit 21 is linear polarizedlight, for example, it is possible to convert the excitation light intocircular polarized light (right circular polarized light and leftcircular polarized light).

As described above, in a state where the alkaline metal atoms in the gascell 31 are subjected to Zeeman splitting due to the magnetic field ofthe coil 35, when the linear polarized excitation light is emitted tothe alkaline metal atoms, the alkaline metal atoms separately existevenly in the plurality of levels where the alkaline metal atoms aresubjected to Zeeman splitting, due to an interaction between theexcitation light and alkaline metal atoms. As a result, since the numberof alkaline metal atoms in a desirable energy level is relativelysmaller than the number of alkaline metal atoms in the other energylevel, the number of atoms for realizing the desirable EIT phenomenon isdecreased, the desirable EIT signal is decreased, and as a result,oscillation characteristics of the atomic oscillator 1 are degraded.

Meanwhile, as described above, in a state where the alkaline metal atomsin the gas cell 31 are subjected to Zeeman splitting due to the magneticfield of the coil 35, when the circular polarized excitation light isemitted to the alkaline metal atoms, it is possible to relativelyincrease the number of alkaline metal atoms in a desirable energy levelto be relatively greater than the number of alkaline metal atoms in theother energy level, among the plurality of levels where the alkalinemetal atoms are subjected to Zeeman splitting, due to an interactionbetween the excitation light and alkaline metal atoms. Accordingly, thenumber of atoms for realizing the desirable EIT phenomenon is increased,the desirable EIT signal is increased, and as a result, oscillationcharacteristics of the atomic oscillator 1 can be improved.

In the embodiment, the optical component 41 has a circular disk shape.Accordingly, it is possible to rotate the optical component 41 around anaxis line parallel with the optical axis (axis a) in a state of beingengaged with a penetration hole (not shown) formed on the base plate 51which will be described later. A shape of the optical component 41 in aplan view is not limited thereto, and may be a polygon such as a squareor a pentagon, for example.

The optical components 42 and 43 are disposed on the second unit 3 sidewith respect to the optical component 41.

The optical components 42 and 43 are respectively neutral densityfilters (ND filters). Accordingly, it is possible to adjust (decrease)the intensity of the excitation light LL incident on the gas cell 31.Therefore, even when the amount of output of the light emitting unit 21is great, it is possible to set the excitation light incident on the gascell 31 as desirable light intensity. In the embodiment, the intensityof the excitation light converted into the circular polarized light bythe optical component 41 described above is adjusted by the opticalcomponents 42 and 43.

In the embodiment, the optical components 42 and 43 respectively have aplate shape. A shape of the respective optical components 42 and 43 in aplan view is a circle. Accordingly, it is possible to rotate the opticalcomponents 42 and 43 around an axis line parallel with the optical axis(axis a) in a state of being engaged with a penetration hole (not shown)formed on the base plate 51 which will be described later.

A shape of the optical components 42 and 43 in a plan view is notlimited thereto, and may be a polygon such as a square or a pentagon,for example.

The optical components 42 and 43 may have equivalent or differentdimming rates.

The upper sides and the lower sides of the respective optical components42 and 43 may have different dimming rates in a continuous or stepwisemanner. In this case, it is possible to adjust the dimming rates of theexcitation light by adjusting the positions of the optical components 42and 43 in a vertical direction with respect to the external package 5.

The respective optical components 42 and 43 may have different dimmingrates in a continuous or stepwise manner, in a circumferentialdirection. In this case, it is possible to adjust the dimming rates ofthe excitation light by rotating the optical components 42 and 43. Inthis case, the rotation centers of the optical components 42 and 43 maybe deviated with respect to the axis a.

Either optical component among the optical components 42 and 43 may beomitted. In addition, when the output of the light emitting unit 21 isan appropriate amount, both of the optical components 42 and 43 can beomitted.

The kinds, the disposed order, or the number of the optical components41, 42, and 43 are not limited. For example, the optical components 41,42, and 43 are not limited to a λ/4 wavelength plate or a neutraldensity filter, and a lens or a polarizing plate may be used.

External Package

As shown in FIG. 4, the external package 5 includes the base plate(substrate) 51 which supports the support plate 7 and the opticalcomponents 41 to 43, and a cover member 52 which is provided so as tocover contained materials such as the first unit 2, the second unit 3,the first substrate 81, the second substrate 82, the third substrate 83,the support plate 7, and the optical components 41 to 43, with respectto the base plate 51. The base plate 51 and the cover member 52 arefixed to each other with an adhesive (not shown), for example.

The first substrate 81, the second substrate 82, and the third substrate83 are separated from each other, and are held to be separated from thebase plate 51 by a plurality of conductive pins 18, in a state of beingarranged in a thickness direction (vertical direction in FIG. 4)thereof.

Each conductive pin 18 penetrates the base plate 51 and is protruded tothe outside of the external package 5, and electrically connects theexternal portion, and the first substrate 81, the second substrate 82,and the third substrate 83, directly or indirectly by the protrudedportion.

The configuration material of the external package is not particularlylimited, and ceramics, metals, or resins can be used, for example.

Support Plate

As shown in FIG. 4, the support plate 7 includes a first plate portion71 which supports the first unit 2, a second plate portion 72 whichsupports the second unit 3, and a pair of connection portions 73 whichconnect the first plate portion 71 and the second plate portion 72 toeach other. The second plate portion 72 is positioned at the upperportion with respect to the first plate portion 71, that is, at thesecond unit 3 side. Since a penetration hole 74 is formed on the supportplate 7, the pair of the connection portions 73 are formed. The supportplate 7 is a member which supports the first unit 2 and the second unit3 at the same surface side (upper surface side) and is mounted on(connected to) the upper portion of the base plate 51 at the lowersurface side.

The upper surface of the first plate portion 71 supports the first unit2, and the lower surface thereof is fixed to the base plate 51. Theupper surface of the second plate portion 72 supports the second unit 3.The lower surface of the second plate portion 72 is separated from thebase plate 51. The optical components 41, 42, and 43 are disposed in theposition of the penetration hole 74.

Since the second unit 3 is separated from the base plate 51 by thesupport plate 7, it is possible to prevent direct heat transfer from thebase plate 51 to the second unit 3. Therefore, the atomic oscillator 1having excellent reliability is obtained.

The pair of connection portions 73 are provided to be separated fromeach other. Accordingly, it is possible to decrease a cross-sectionalarea of the connection portions 73, compared to a case where theconnection portion 73 is configured with one piece of plate, forexample. Therefore, as the cross-sectional area is small, it is possibleto decrease quantity of heat conduction from the first plate portion 71to the second plate portion 72. Thus, the atomic oscillator 1 havingexcellent reliability is obtained.

The configuration material of the support plate 7 is not particularlylimited, and ceramics, metals, or resins can be used, but metals arepreferable among these.

Control Unit

The control unit 6 shown in FIG. 1 has a function of controlling each ofthe heater 33, the coil 35, the light emitting unit 21, and the Peltierelements 24 and 46.

In the embodiment, the control unit 6 is configured with a plurality ofintegrated circuit (IC) chips mounted on the first substrate 81, thesecond substrate 82, and the third substrate 83.

As shown in FIG. 1 and FIG. 7, the control unit 6 includes a excitationlight control unit (light emitting unit control unit) 61 which controlsthe frequencies of the resonance light beams 1 and 2 of the lightemitting unit 21, the cell temperature control unit 62 which controlsthe temperature of the alkaline metal in the gas cell 31 (temperature ofthe gas cell 31), the magnetic field control unit 63 which controls themagnetic field applied to the gas cell 31, the light emitting unittemperature control unit 64 which controls the temperature of the lightemitting unit 21, the package temperature control unit 65 which controlsthe temperature of the second package 36, a sweep circuit 69, and a biascurrent generation unit 56 which generates bias current to be suppliedto the light emitting unit 21 and outputs the bias current to the lightemitting unit 21.

The excitation light control unit 61 includes the light receivingcircuit 68 which processes the light receiving signal output from thelight receiving unit 38, a crystal oscillator (oscillation circuit) 13,a multiplier 611 which is electrically connected to an output terminalof the crystal oscillator, and an amplifier/attenuator 612 which iselectrically connected to the multiplier 611. As the multiplier 611, aphase locked loop (PLL) synthesizer circuit or the like can be used, forexample. The multiplier 611 and the amplifier/attenuator 612 configure ahigh frequency current generation unit 610 which generates highfrequency current to be supplied to the light emitting unit 21 andoutputs the high frequency current to the light emitting unit 21. In thespecification, the high frequency is a frequency equal to or higher than10 MHz.

The bias current generation unit 56 has a function of converting thevoltage to the DC current. That is, the bias current generation unit 56includes a voltage current conversion circuit (VI conversion circuit)which converts the voltage to the DC current.

Herein, the connector 194 is installed on the first substrate 81, andthe connector 194 and the light emitting unit 21 are electricallyconnected to each other by a flexible connector (not shown). Theconnector 194 and the high frequency current generation unit 610 areelectrically connected to each other by a wire 91 of the first substrate81. The connector 194 and the bias current generation unit 56 areelectrically connected to each other by a wire 92 of the first substrate81.

The connector 194 is a first output unit from which the high frequencycurrent generated by the high frequency current generation unit 610 isoutput, and is a second output unit from which the bias currentgenerated by the bias current generation unit is output. The biascurrent and the high frequency current output from the connector 194 aretransmitted to the light emitting unit 21 separately or in a synthesizedmanner.

The control unit 6 includes an analog circuit 67 which includes thecrystal oscillator 13 and the light receiving circuit 68 and controlsthe EIT signal, and a digital circuit 66 which controls the analogcircuit 67 and the excitation light control unit 61. Many parts (somepart) of the constituent elements of the analog circuit 67 and theconstituent elements of the excitation light control unit 61 areoverlapped with each other.

The cell temperature control unit 62 controls the driving of the heater(heating unit) 33, that is, controls the electrical connection to theheater 33, based on the detected result of the temperature sensor 34.Accordingly, it is possible to maintain the temperature of the gas cell31 in a range of a desirable temperature.

The magnetic field control unit 63 controls the electrical connection tothe coil 35 so that the magnetic field generated by the coil 35 isconstant.

The light emitting unit temperature control unit 64 controls the drivingof the Peltier element 24, that is, controls the electrical connectionto the Peltier element 24, based on the detected result of thetemperature sensor 25. Accordingly, it is possible to maintain thetemperature of the light emitting unit 21 in a range of a desirabletemperature.

The package temperature control unit 65 controls the driving of thePeltier element 46, that is, controls the electrical connection to thePeltier element 46, based on the detected result of the temperaturesensor 47. Accordingly, it is possible to maintain the temperature ofthe second package 36 in a range of a desirable temperature.

Herein, many parts of the excitation light control unit 61 and theanalog circuit 67 are overlapped with each other and the excitationlight control unit and the analog circuit are controlled substantiallyin the same manner, and accordingly, the control operation of theexcitation light control unit 61 will be representatively described,hereinafter.

The excitation light control unit 61 controls the driving (EIT signal)of the light emitting unit 21, that is, controls the frequencies of theresonance light beams 1 and 2 emitted from the light emitting unit 21,based on the detected result of the light receiving unit 38 and thelight receiving circuit 68. More specifically, the excitation lightcontrol unit 61 controls the frequencies of the resonance light beams 1and 2 emitted from the light emitting unit 21 so that the difference infrequencies (ω1−ω2) becomes the alkaline metal specific frequency ω0,based on the detected result of the light receiving unit 38 and thelight receiving circuit 68.

The excitation light control unit 61 synchronizes and adjusts theoscillation frequency (resonance frequency) of the crystal oscillator 13and outputs the oscillation frequency as the output signal of the atomicoscillator 1, based on the detected result of the light receiving unit38 and the light receiving circuit 68. It is possible to use avoltage-controlled crystal oscillator as the crystal oscillator 13, forexample.

Herein, regarding the adjustment of the oscillation frequency of thecrystal oscillator 13, a case where the alkaline metal specificfrequency ω0 is 9.2 GHz, the oscillation frequency of the crystaloscillator 13 is maintained at 10 kHz, and the signal at 10 kHz isoutput as an output signal of the atomic oscillator 1, is described as aspecific example.

First, the signal (frequency: 10 kHz) output from the crystal oscillator13 is multiplied to 4.6×10⁵ times (frequency: 4.6 GHz) by the multiplier611, amplified and attenuated by the amplifier/attenuator 612, and isoutput as high frequency current from the amplifier/attenuator 612.

Meanwhile, the voltage is converted into the DC current and is output asthe bias current by the bias current generation unit 56.

The high frequency current and the bias current are synthesized andsubjected to frequency modulation, and then is supplied to the lightemitting unit 21. The light emitting unit 21 is driven by the signalsubjected to the frequency modulation and emits the excitation light LLdescribed above, and the excitation light LL penetrating the inside ofthe gas cell 31 is received, that is, subjected to photoelectricconversion by the light receiving unit 38. The current output from thelight receiving unit 38 is converted into the voltage and amplified, bythe light receiving circuit 68. That is, in the light receiving unit 38and the light receiving circuit 68, the intensity of the excitationlight LL is detected, and the excitation light control unit 61 performsa process based on the detected result (EIT signal). As long as theintensity of the EIT signal is equal to or greater than a thresholdvalue, when the intensity of the EIT signal and a preset threshold valueare compared to each other, the light receiving circuit 68 of theexcitation light control unit 61 transmits a signal showing that theintensity of the EIT signal is equal to or greater than a thresholdvalue, to the digital circuit 66. When the intensity of the EIT signalis equal to or greater than a threshold value, the light receivingcircuit 68 of the excitation light control unit 61 constantly transmitsthe signal showing that the intensity of the EIT signal is equal to orgreater than a threshold value, to the digital circuit 66. When thedigital circuit 66 receives the signal showing that the intensity of theEIT signal is equal to or greater than a threshold value, the digitalcircuit determines that the crystal oscillator 13 oscillates at 10 kHz,is released from the sweep circuit 69, and fixes the oscillationfrequency of the crystal oscillator 13 to the atomic resonancefrequency.

However, the oscillation frequency of the crystal oscillator 13 changeswith time for a long time, due to the quartz crystal of the crystaloscillator 13 which degrades with time. Accordingly, in order to fix theoscillation frequency to the atomic resonance frequency, it is necessaryto sweep the oscillation frequency of the crystal oscillator 13 by thesweep circuit 69 and to find the frequency for output the EIT signal.

When adjusting the oscillation frequency of the crystal oscillator 13,the excitation light control unit 61 changes the oscillation frequencyof the crystal oscillator 13 to a frequency close to 10 kHz by the sweepcircuit 69, and transmits the signal showing that the intensity of theEIT signal is equal to or greater than a threshold value to the digitalcircuit 66, when the intensity of the EIT signal is equal to or greaterthan a threshold value, by comparing the intensity of the EIT signal andthe threshold value to each other as described above. When the digitalcircuit 66 receives the signal showing that the intensity of the EITsignal is equal to or greater than a threshold value, the digitalcircuit determines that the crystal oscillator 13 oscillates at 10 kHz,and is released from the sweep circuit 69, and fixes the oscillationfrequency of the crystal oscillator 13. Accordingly, a state in whichthe crystal oscillator 13 oscillates at 10 kHz is maintained.

Power Terminal, Power Circuit, and Boosting Circuit

As shown in FIG. 1 and FIG. 7, the atomic oscillator 1 includes a powerterminal 15 which is provided on the first substrate 81 and iselectrically connected to a power 16, and a power voltage is applied tothe power terminal 15 from the power 16. The power voltage output fromthe power 16 is applied to predetermined units from the power terminal15. The power 16 may be embedded in or detachable from the atomicoscillator 1, or may be a power at the outside of the atomic oscillator1.

The atomic oscillator 1 includes a power circuit 17 which is provided onthe first substrate 81 and is electrically connected to the powerterminal 15. In the power circuit 17, the power voltage is convertedinto voltages having various predetermined sizes, and each voltage isapplied to predetermined units.

The power terminal 15 and the power circuit 17 are respectivelyelectrically connected to a connector 191 provided on the firstsubstrate 81. The power voltage and the voltage converted by the powercircuit 17 are, respectively, applied to each unit provided on thesecond substrate 82 through the connector 191 and a connector 192 (seeFIG. 4) which will be described later, and applied to each unit providedon the third substrate 83 through the connectors 191 and 192 and aconnector 193 (see FIG. 4) which will be described later.

Herein, the connector 191 is preferably provided in the vicinity of thepower terminal 15. The power circuit 17 is preferably provided in thevicinity of the power terminal 15. The power circuit 17 is preferablyprovided in the vicinity of the connector 191. Accordingly, it ispossible to supply the current to be supplied to the power terminal 15with a short wire, from the power terminal 15 to each unit provided onthe second substrate 82 and each unit provided on the third substrate83. Therefore, it is possible to decrease power loss.

A fuse may be, for example, respectively provided between the powerterminal 15 and the power circuit 17, and between the power terminal 15and the connector 191.

The atomic oscillator 1 includes a boosting circuit 14 which is providedon the third substrate 83 and increases the voltage applied to theheater 33. The boosting circuit 14 is positioned in the middle of thepower line between the power terminal 15 and the heater 33, an inputterminal of the boosting circuit 14 is electrically connected to thepower terminal 15, and an output terminal of the boosting circuit 14 iselectrically connected to the heater 33. Accordingly, the power voltageis increased by the boosting circuit 14 and is applied to the heater 33.Therefore, it is possible to maintain the constant power supplied to theheater 33, and to decrease the current flowing through the heater 33.Thus, it is possible to decrease the magnetic field generated by thecurrent flowing through the heater 33 when electrically connected to theheater 33, and to prevent or suppress a negative effect of the magneticfield on the inside of the gas cell 31.

The boosting circuit 14 is not particularly limited, as long as it canincrease the voltage, and preferably has a switching function such as aswitching regulator, for example. It is possible to realize highefficiency and low cost by using the boosting circuit having a switchingfunction.

When the boosting circuit having a switching function is used as theboosting circuit 14, a switching frequency is not particularly limited,is appropriately set with the conditions, but is preferably from 10 kHzto 10 MHz, and more preferably from 100 kHz to 3 MHz. Herein, themagnetic field generated by the electrical connection to the heater 33includes a component dependent to the switching frequency of theboosting circuit 14. Meanwhile, since the light emitting unit 21 isdriven by a signal subjected to frequency modulation at a low frequency(for example, approximately 100 Hz) and emits the excitation light LL,the atomic resonance is easily affected with the magnetic fieldincluding a frequency component close to the frequency for frequencymodulation. Accordingly, the switching frequency is preferably separatedfrom the frequency for frequency modulation. Therefore, when theswitching frequency is lower than the lower limit value, the magneticfield generated by the electric connection to the heater 33 negativelyaffects the atomic resonance, depending on the other conditions. Whenthe switching frequency is close to an output frequency, the atomicresonance is negatively affected, for example, by generating noise.

An amplification factor of the voltage of the boosting circuit 14 is notparticularly limited and is appropriately set with the conditions, butis preferably from 2 times to 5 times, and more preferably from 3 timesto 4.5 times. The amplification factor of the voltage is a valueobtained by dividing the amplified voltage by the voltage before theamplification. When the amplification factor of the voltage is less thanthe lower limit value, the magnetic field generated by the electricalconnection to the heater 33 may become excessively large, depending onthe other conditions. When the amplification factor of the voltage isgreater than the upper value, a high-voltage member is necessary, a sizeof a device may increase, the cost may increase, or more noise may begenerated, depending on the other conditions.

The current supplied to the heater 33 is not particularly limited and isappropriately set with the conditions, but is preferably equal to orsmaller than 1.5 A, more preferably equal to or smaller than 300 mA, andeven more preferably from 1 mA to 300 mA. The voltage applied to theheater 33 is not particularly limited and is appropriately set with theconditions, but is preferably from 6 V to 15 V, and more preferably from8 V to 14 V.

The output terminal of the boosting circuit 14 is not electricallyconnected to the other portions such as the light emitting unit 21, thelight receiving unit 38, the excitation light control unit 61, the celltemperature control unit 62, the light emitting unit temperature controlunit 64, and the package temperature control unit 65. That is, theboosting circuit 14 is used to be dedicated to the heater 33.Accordingly, it is possible to freely set each parameter of the boostingcircuit 14 so as to be optimal with respect to the heater 33.

The effects of providing the boosting circuit 14 are as follows.

First, it is possible to decrease the power consumption by decreasingthe power voltage. By increasing the power to be applied to the heater33 by the boosting circuit 14, it is possible to maintain the constantpower supplied to the heater 33, to decrease the current flowing throughthe heater 33, and accordingly, it is possible to decrease the magneticfield generated by the heater 33 by the electrical connection to theheater 33. Therefore, it is possible to prevent or suppress the negativeeffect of the magnetic field generated by the heater 33 on the inside ofthe gas cell 31, to stabilize the magnetic field generated in theinternal space S of the gas cell 31, and to improve the accuracy of theoscillation frequency of the atomic oscillator 1. In addition, it ispossible to simplify the magnetic shield.

First Substrate, Second Substrate, and Third Substrate

Hereinafter, the first substrate 81, the second substrate 82, and thethird substrate 83 will be described based on FIGS. 1, 4, 6, and 7.

The first substrate 81, the second substrate 82, and the third substrate83 have wires (not shown), and have a function of electricallyconnecting each electronic component of the control unit 6 separatelymounted on the first substrate 81, the second substrate 82, and thethird substrate 83, and each connector (not shown) through the wires.Each connector is a member which electrically connects the first unit 2and the second unit 3, and the first substrate 81, the second substrate82, and the third substrate 83 to each other.

Various printed circuit boards can be used as the first substrate 81,the second substrate 82, and the third substrate 83, and a substrateincluding a rigid portion, for example, a rigid substrate or a rigidflexible substrate is preferably used.

The control unit 6 is separately installed on one surface (surface onthe upper side in FIG. 4) of the first substrate 81, the secondsubstrate 82, and the third substrate 83.

That is, the power circuit 17, the excitation light control unit 61including the high frequency current generation unit 610, the analogcircuit 67 including the light receiving circuit 68, and the biascurrent generation unit 56 are installed on the first substrate 81. Thepower terminal 15 electrically connected to the power 16, the powercircuit 17 electrically connected to the power terminal 15, and theconnectors 194 and 195 are installed on the first substrate 81.

The light emitting unit temperature control unit 64, the celltemperature control unit 62, and the digital circuit 66 are installed onthe second substrate 82.

The boosting circuit 14 and the package temperature control unit 65 areinstalled on the third substrate 83. The boosting circuit 14 isinstalled on the third substrate 83.

Herein, when the relative sizes of the current flowing through eachcircuit (each unit) provided on the first substrate 81, the secondsubstrate 82, and the third substrate 83 are divided into three stagesof “large”, “medium”, and “small”, the size of the current flowingthrough each circuit of the first substrate 81 is set to “small”, thesize of the current flowing through each circuit of the second substrate82 is set to “medium”, and the size of the current flowing through eachcircuit of the third substrate 83 is set to “large”. As described above,it is possible to decrease interference between each circuit, bydividing the substrates by the size of the current (or size of thefrequency). Therefore, it is possible to reliably detect the minute EITsignal, and to provide the atomic oscillator 1 with high accuracy.

As shown in FIGS. 4 and 6, the shape of the first substrate 81, thesecond substrate 82, and the third substrate 83 is not particularlylimited, and is a rectangle, in the embodiment.

The dimension of the first substrate 81, the second substrate 82, andthe third substrate 83 is not particularly limited. In the embodiment,the size of the first substrate 81 is largest, and the second substrate82 and the third substrate 83 have the same size as each other.

An opening 811 is formed on a portion of the first substrate 81 wherethe second substrate 82 and the third substrate 83 are not positioned.The first unit 2 and the second unit 3 are disposed in the opening 811.

The first substrate 81, the second substrate 82, and the third substrate83 are arranged along a thickness direction thereof at predeterminedintervals. In this case, the first substrate 81, the second substrate82, and the third substrate 83 are disposed in this order from the lowerside to the upper side in the drawing, the first substrate 81 and thesecond substrate 82 are separated from each other, and the secondsubstrate 82 and the third substrate 83 are separated from each other.That is, at least some parts of the first substrate 81, the secondsubstrate 82, and the third substrate 83 are overlapped with each other,when seen from the thickness direction, that is, in a plan view. In theconfiguration shown in the drawing, the entire second substrate 82 isoverlapped with the first substrate 81 in a plan view, the entire thirdsubstrate 83 is overlapped with the first substrate 81 in a plan view,and the entirety of the second substrate 82 and the third substrate 83are overlapped with each other in a plan view. Therefore, it is possibleto miniaturize the atomic oscillator 1.

The connector (first connection terminal) 191 electrically connected tothe wire of the first substrate 81 is installed on the first substrate81, the connector (second connection terminal) 192 electricallyconnected to the wire of the second substrate 82 is installed on thesecond substrate 82, and the connector (third connection terminal) 193electrically connected to the wire of the third substrate 83 isinstalled on the third substrate 83. The connector 191 and the connector192 are detachably connected to each other, and the connector 191 andthe connector 192 are electrically connected to each other, in a stateof being connected to each other. In the same manner as described above,the connector 192 and the connector 193 are detachably connected to eachother, and the connector 192 and the connector 193 are also electricallyconnected to each other, in a state of being connected to each other.Accordingly, in a state where the connector 191 and the connector 192are connected to each other and the connector 192 and the connector 193are connected to each other, the first substrate 81, the secondsubstrate 82, and the third substrate 83 are electrically connected toeach other.

The connector 191, the connector 192, and the connector 193 areoverlapped with each other, when seen from the thickness direction ofthe first substrate 81, the second substrate 82, and the third substrate83, that is, in a plan view. Accordingly, it is possible to supply thecurrent to be supplied to the power terminal 15 with a short wire, fromthe power terminal 15 to each unit provided on the second substrate 82and each unit provided on the third substrate 83, through the connectors191, 192, and 193. Therefore, it is possible to decrease power loss.

The order of the first substrate 81, the second substrate 82, and thethird substrate 83 is not limited to the order described above, and theorder thereof may be set as the order of the first substrate 81, thethird substrate 83, and the second substrate 82, the order of the thirdsubstrate 83, the first substrate 81, and the second substrate 82, theorder of the third substrate 83, the second substrate 82, and the firstsubstrate 81, the order of the second substrate 82, the first substrate81, and the third substrate 83, and the order of the second substrate82, the third substrate 83, and the first substrate 81, from the lowerside to the upper side in FIGS. 4 and 6.

Other electronic components than the components described above may bemounted on the first substrate 81, the second substrate 82, and thethird substrate 83.

Position Relationship of Each Unit Installed on First Substrate

As shown in FIG. 7, first, the light emitting unit 21, the gas cell 31,and the light receiving unit 38 are arranged in the X axis direction,the light emitting unit 21 is disposed on the positive side of the gascell 31 in the X axis direction, and the light receiving unit 38 isdisposed on the negative side of the gas cell 31 in the X axisdirection.

The light receiving circuit 68 and the connector 195 are disposed on thenegative side of the light receiving unit 38 in the X axis direction.The light receiving circuit 68 and the connector 195 are arranged in theX axis direction with the light emitting unit 21, the gas cell 31, andthe light receiving unit 38, and are disposed in the order of the lightreceiving circuit 68 and the connector 195, to the negative side in theX axis direction. The connector 195 is disposed in a range in thevicinity of the light receiving unit 38 and the light receiving circuit68, and in the Y axis direction of the second unit 3.

The bias current generation unit 56 and the connector 194 are disposedon the positive side in the X axis direction of the light emitting unit21. The bias current generation unit 56 and the connector 194 arearranged in the X axis direction (direction in which the gas cell 31 andthe light emitting unit 21 are arranged) with the light emitting unit21, the gas cell 31, and the light receiving unit 38, and are disposedin the order of the connector 194 and the bias current generation unit56, to the positive side in the X axis direction. Accordingly, the lightemitting unit 21, the gas cell 31, the light receiving unit 38, and thelight receiving circuit 68 are disposed between the connector 195 andthe connector 194.

The high frequency current generation unit 610 is arranged in the Y axisdirection with the gas cell 31, the light emitting unit 21, and theconnector 194, and are disposed on the negative side in the Y axisdirection of the gas cell 31, the light emitting unit 21, and theconnector 194. That is, the high frequency current generation unit 610is deviated from a linear line 95 connecting the center of the gas cell31 and the center of the light emitting unit 21. Accordingly, it ispossible to decrease the dimension of the device in the direction of thelinear line 95 (X axis direction) and to realize miniaturization,compared to a case where the high frequency current generation unit 610is disposed on the linear line 95.

The connector 194 is disposed in a range in the vicinity of the lightemitting unit 21, the bias current generation unit 56, and the highfrequency current generation unit 610, and in the Y axis direction ofthe second unit 3.

The connector 194 is disposed on the light emitting unit 21 side withrespect to the high frequency current generation unit 610.

The dimension of the first substrate 81 is not particularly limited andis appropriately set with the conditions, but one length of the firstsubstrate 81 is preferably equal to or smaller than 100 mm, and morepreferably from 5 mm to 70 mm. Therefore, it is possible to provide thesmall-sized atomic oscillator 1.

A length L1 of the wire 91 between the connector 194 and an outputterminal of the high frequency current generation unit 610 is notparticularly limited and is appropriately set with the conditions, butis preferably equal to or smaller than 5 mm, and more preferably from0.5 mm to 3 mm. When the L1 is greater than the upper limit value, anattenuation amount of the high frequency current may increase, dependingon the other conditions.

A length L2 of the wire 92 between the connector 194 and an outputterminal of the bias current generation unit 56 is not particularlylimited and is appropriately set with the conditions, but is preferablyequal to or smaller than 5 mm, and more preferably from 0.5 mm to 3 mm.When the L2 is greater than the upper limit value, an amount of thenoise mixed with the bias current may increase, depending on the otherconditions.

A length L3 of the wire 93 between the connector 195 and an outputterminal of the light receiving circuit 68 is not particularly limitedand is appropriately set with the conditions, but is preferably equal toor smaller than 5 mm, and more preferably from 0.5 mm to 3 mm. When theL3 is greater than the upper limit value, an amount of the noise mixedwith the light receiving signal may increase, depending on the otherconditions.

As described above, according to the atomic oscillator 1, by employingthe disposition and the dimension described above, it is possible todecrease the length of the wire between the connector 195 and the lightreceiving unit 38 and to decrease the length of the wire between thelight receiving circuit 68 and the light receiving unit 38, andtherefore it is possible to decrease the amount of the noise mixed withthe light receiving signal. In addition, it is possible to decrease thelength of the wire between the connector 194 and the light emitting unit21 and to decrease the length of the wire between the high frequencycurrent generation unit 610 and the light emitting unit 21, andtherefore it is possible to decrease the attenuation amount of the highfrequency current. Further, it is possible to decrease the length of thewire between the bias current generation unit 56 and the light emittingunit 21, and it is possible to decrease the amount of the noise mixedwith the bias current. Accordingly, it is possible to improve an SNratio of the EIT signal, and to reliably detect the EIT signal.Therefore, it is possible to provide the atomic oscillator 1 with highaccuracy.

By employing the disposition and the dimension described above, it ispossible to miniaturize the atomic oscillator 1.

2. Electronic Device

The atomic oscillator described above can be introduced to variouselectronic devices. Such electronic devices have excellent reliability.

Hereinafter, the electronic device according to the invention will bedescribed.

FIG. 8 is a schematic view of a system configuration when the atomicoscillator according to the invention is used in a positioning systemusing a GPS satellite.

A positioning system 100 shown in FIG. 8 is configured with a GPSsatellite 200, abase station device 300, and a GPS receiver 400.

The GPS satellite 200 transmits positioning information (GPS signal).

The base station device 300, for example, includes a receiver 302 whichreceives the positioning information from the GPS satellite 200 throughan antenna 301 installed at an electronic reference point (GPScontinuous observation station) with high accuracy, and a transmitter304 which transmits the positioning information received by the receiver302 through an antenna 303.

Herein, the receiver 302 is an electronic device including the atomicoscillator 1 according to the invention described above, as a referencefrequency oscillation source. The receiver 302 has excellentreliability. The positioning information received by the receiver 302 istransmitted by the transmitter 304 in real time.

The GPS receiver 400 includes a satellite receiving unit 402 whichreceives the positioning information from the GPS satellite 200 throughan antenna 401, and a base station receiving unit 404 which receives thepositioning information from the base station device 300 through anantenna 403.

3. Moving Object

FIG. 9 is a diagram showing an example of a moving object according tothe invention.

In this drawing, a moving object 1500 includes a car body 1501 and fourwheels 1502, and is configured so as to rotate the wheels 1502 with apower source (engine, not shown) provided on the car body 1501. Theatomic oscillator 1 is embedded in the moving object 1500.

According to the moving object, it is possible to exhibit excellentreliability.

The electronic device including the atomic oscillator according to theinvention (quantum interference device according to the invention) isnot particularly limited to the above, and examples thereof include amobile phone, a digital still camera, an ink jet type dischargingapparatus (for example, ink jet printer), a personal computer (amobile-type personal computer or a laptop-type personal computer), atelevision, a video camera, a video recorder, a car navigationapparatus, a pager, an electronic organizer (including a communicationfunction), an electronic dictionary, a calculator, an electronic gamedevice, a word processer, a work station, a video phone, a securitymonitor, electronic binoculars, a POS terminal, medical equipment (forexample, an electronic thermometer, a blood pressure meter, a bloodglucose meter, an ECG measuring device, a ultrasound diagnostic device,and an electronic endoscope), a fish finder, a variety of measurementequipment, a meter (for example, meters for vehicles, aircraft, andships), a flight simulator, terrestrial digital broadcasting, a mobilephone base station, and the like.

Hereinabove, the quantum interference device, the atomic oscillator, theelectronic device, and the moving object according to the invention havebeen described based on the embodiments shown in the drawing, but theinvention is not limited thereto.

In the quantum interference device, the atomic oscillator, theelectronic device, and the moving object according to the invention, theconfiguration of each unit can be replaced with the arbitraryconfiguration which exhibits the same functions, or the arbitraryconfiguration can be added thereto.

In the invention, the arbitrary configurations of the embodimentsdescribed above may be combined with each other.

In the invention, the structure of the atomic oscillator (quantuminterference device) is not limited to the configuration of theembodiments described above.

For example, in the embodiments described above, the structure in whichthe gas cell is disposed between the light emitting unit and the lightreceiving unit has been described as an example, but there is nolimitation, and the light emitting unit and the light receiving unit maybe disposed on the same side with respect to the gas cell, and the lightreflected by a surface on the side opposite to the light emitting unitand the light receiving unit of the gas cell, or by a mirror provided onthe side opposite to the light emitting unit and the light receivingunit of the gas cell may be detected by the light receiving unit.

In the embodiments described above, three substrates of the firstsubstrate, the second substrate, and the third substrate are provided asthe substrates including the wires, but there is no limitation, and thenumber of the substrates may be one, two, or four or more.

In the embodiments described above, the structure in which the firstunit and the second unit are installed on the base plate of the externalpackage has been described as an example, but there is no limitation,and the first unit and the second unit may be installed on the firstsubstrate, for example.

In the embodiments described above, the atomic oscillator using thequantum interference effect with two kinds of light beams havingdifferent wavelengths has been described as an example, but there is nolimitation, and an atomic oscillator using a double resonance phenomenonwith light or microwaves may be used.

The entire disclosure of Japanese Patent Application No. 2013-263492,filed Dec. 20, 2013 is expressly incorporated by reference herein.

What is claimed is:
 1. A quantum interference device comprising: a gascell in which metal atoms are sealed; a light emitting unit which emitslight to the gas cell; a light receiving unit which receives the lightpenetrating the gas cell and outputs a light receiving signal; an inputunit which inputs the light receiving signal; a light receiving circuitwhich processes the light receiving signal output from the input unit; ahigh frequency current generation unit which is arranged with the lightemitting unit in a line, and generates high frequency current; and afirst output unit which outputs the high frequency current output fromthe high frequency current generation unit to the light emitting unit,wherein the gas cell is disposed between the input unit and the firstoutput unit.
 2. The quantum interference device according to claim 1,further comprising: a bias current generation unit which is arrangedwith the light emitting unit in a line, and generates bias current to besupplied to the light emitting unit; and a second output unit whichoutputs the bias current output from the bias current generation unit tothe light emitting unit, wherein the gas cell is disposed between theinput unit and the second output unit.
 3. The quantum interferencedevice according to claim 1, wherein the high frequency currentgeneration unit is deviated from a linear line connecting the gas celland the light emitting unit.
 4. The quantum interference deviceaccording to claim 1, wherein the high frequency current generation unitand the gas cell are arranged in a line.
 5. The quantum interferencedevice according to claim 1, wherein the first output unit is arrangedin a direction in which the gas cell and the light emitting unit arearranged in a line, and is disposed on the light emitting unit side withrespect to the high frequency current generation unit.
 6. An atomicoscillator comprising the quantum interference device according toclaim
 1. 7. An electronic device comprising the quantum interferencedevice according to claim
 1. 8. A moving object comprising the quantuminterference device according to claim 1.